A synthetic wastewater containing glucose as the sole source of carbon was used to assay glucoseacclimatized anaerobic digester sludge in batch-tests for its potential to carry out ammonification (nitrate--> ammonium), denitrification (nitrate -->nitrogen gas) and to continue anaerobic digestion processes at various nitrate loads. Nitrate-->ammonium reduction activity was found to increase with decrease in the initial nitrate load. This activity appeared to take place principally during the acidogenesis of the glucose. Nitrate/nitrite loss after the fermentation process was essentially through denitrification. The denitrification capacity of the anaerobic sludge used was very high. Up to 80% of added nitrate was denitrified. The presence of nitrate or nitrite enhanced the fermentation of glucose to acetic acid but inhibited the production of propionic acid and methane. This inhibition was not observed after the complete reduction of nitrate and nitrite.
Two laboratory upflow aerobic and anaerobic filters fed with synthetic wastewaters were used to study firstly the effects of aeration rate on the nitrification of anaerobically pre-treated effluents and secondly the effects of recycle-to-influent ratios on methane production rate, denitrification and nitrification performances of a combined aerobic and anaerobic wastewater treatment process. Nitrification of anaerobically pre-treated effluent was accompanied by aerobic post-treatment for residual COD removal. A comparison of nitrification performances using autotrophic medium and anaerobically pre-treated effluents (containing 1203 mg COD 1−1) with the same ammonia nitrogen concentration of about 300 mg NH4-N 1−1 showed that 3% of added ammonia nitrogen was assimilated by autotrophic nitrifiers during nitrification of the autotrophic medium while up to 30% was assimilated by both nitrifiers and heterotrophs during organic carbon removal and nitrification of anaerobically pre-treated effluent. Furthermore, it was suspected that significant nitrogen loss through denitrification occured in the aerobic filter especially at low aeration rates. In the study of the combined aerobic-anaerobic system, maximum ammonia nitrogen removal of 70% through denitrification was obtained at recycle-to-influent ratios of 4 and 5. COD removal efficiency in the anaerobic filter decreased from 77 to 60% for recycle-to-influent ratios of zero to 5. Overall COD removal efficiency of the entire system was constant at about 99% due to heterotrophic COD removal in the aerobic filter.
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